The present invention relates to a transmission/reception apparatus and its transmit power control method of a mobile communication using a CDMA system.
A transmission/reception apparatus and its transmit power control method in a conventional mobile communication are explained using FIG. 20. FIG. 1 is a main block diagram showing an outlined configuration of a conventional transmission/reception apparatus.
Frame assembling section 1 multiplexes transmission data with a TPC bit. Spreading section 2 spreads/modulates the multiplexed data and BPF 3 eliminates an unnecessary signal from the spread/modulated signal. Transmission amplifier 4 amplifies the transmission signal stripped of the unnecessary signal. Duplexer 5 controls an input/output signal to/from antenna 6. Antenna 6 radiates the amplified transmission signal.
Antenna 6 receives a transmitted signal. Despreading section 7 demodulates the reception signal. At this time, received quality detecting section 8 detects a received quality by calculating a signal interference ratio (hereinafter referred to as xe2x80x9cSIRxe2x80x9d) from the result of despreading performed by despreading section 7.
TPC bit generating section 9 receives the detection result of received quality detecting section 8 and generates a TPC bit to instruct a far-end station to increase transmit power if the received quality falls 10 below a desired quality and lower transmit power if the received quality equals to or exceeds the desired quality to reduce interference with other users. For example, the TPC bit is set to 1 if the received quality falls below the desired quality and 0 if the received quality equals to or exceeds the desired quality. The TPC bit generated is sent to frame assembling section 1 and multiplexed with transmission data.
Determining section 10 acquires reception data from the demodulated reception signal and at the same time extracts the TPC bit generated and sent by the far-end station and determines whether the TPC bit is 0 or 1. Accumulating section 11 receives the judgment result of determining section 10 and instructs transmission amplifier 4 to increase or decrease transmit power according to the result. It is predetermined that, for example, if the determination result is 0, accumulating section 11 determines that the instruction from the far-end station is to decrease transmit power and decreases the current amount of amplification by 1 dB and if the determination result is 1, accumulating section 11 determines that the instruction from the far-end station is to increase transmit power and increases the current amount of amplification by 1 dB.
In this way, the conventional transmission/reception apparatus and transmit power control method maintain appropriate transmit power by the transmission/reception apparatuses of both the base station and mobile station carrying out transmit power control based on the TPC bit in the reception signal.
However, in the conventional transmission/reception apparatus and transmit power control method, since an amount of the increase or decrease during transmit power control, that is, a range of transmit power to be increased or decreased based on a TPC bit made up of one received bit is a predetermined fixed value (xc2x11 dB in the example above), if this fixed value is too large, it is difficult to control transmit power appropriately and maintain stability when amplitude variations are small (during slow fading), whereas if this fixed value is too small, poor traceability results when there are considerable amplitude variations (during fast fading).
A situation with large amplitude variations occurs, for example, when a compressed mode is used. A system which provides a pause interval such as compressed mode produces a large difference between a control transmit power value and required transmit power value which is a target value.
Moreover, the example above has a TPC bit made up of one bit, and therefore can only transmit or receive two values, that is, xe2x80x9cincrease orxe2x80x9d decrease. Therefore, it is also possible to increase an amount of information that can be transmitted/received by increasing assignment to the TPC bit within one slot and finely control not only an increase or decrease of transmit power but also the amount of the increase or decrease. However, since the number of bits within one slot is fixed, increasing the number of bits used as TPC bits will cause a problem of reducing data transmission efficiency.
Moreover, in the above example, control is limited to increasing or decreasing transmit power even if transmit power is appropriate and it is preferable to maintain the current value, and thus it is not possible to maintain a fixed value, ending up repeating increases and decreases in short cycles centered on an appropriate value.
It is an objective of the present invention to provide a transmission/reception apparatus and its transmit power control method combining trackability during fast fading or when a compressed mode is applied and stability during slow fading without reducing data transmission efficiency.
The transmission/reception apparatus and its transmit power control method in the present invention allows the amplitude of a TPC bit to be set apart from other transmission signals. Especially, using not only the symbol of a TPC bit but also the amplitude as parameters allows the symbol to represent an increase or decrease and the amplitude to represent an amount of the increase or decrease, making it possible for one TPC bit to transmit not only control of a certain amount of increase or decrease of transmit power but also control by increasing or decreasing transmit power by an arbitrary amount of increase or decrease.